A central role for neuronal AMP-activated protein kinase (AMPK) and mammalian target of rapamycin (mTOR) in high-protein diet-induced weight loss

Sustained insulin treatment restoring metabolic status, body weight, and cognition in an anorexia nervosa-like animal model in mice

INTRODUCTION

Anorexia Nervosa (AN) is a psycho-socio-biological disease characterized by severe weight loss as result of dieting and hyperactivity. Effective treatments are scarce, despite its significant prevalence and mortality. AN patients show lower basal insulin levels and increased metabolic clearance, leading to weight loss, cognitive deficits, and hormonal imbalances. Low-dose polymer insulin could potentially reverse these effects by restoring brain function, reducing fear of weight gain, encouraging food intake, and restoring fat depots. This study evaluates an insulin delivery system designed for sustained release and AN treatment.

METHODS

AN-like model was established through dietary restriction (DR). On days 1-25, mice were on DR, and on days 26-31 they were on ad libitum regimen. An insulin-loaded delivery system was administered subcutaneously (1% w/w insulin). The impact of insulin treatment on gene expression in the hippocampus (cognition, regulation of stress, neurogenesis) and hypothalamus (eating behavior, mood) was assessed. Behavioral assays were conducted to evaluate motor activity and cognitive function.

RESULTS

The delivery system demonstrated sustained insulin release, maintaining therapeutic plasma levels. Diet restriction mice treated with the insulin delivery system showed body weight restoration. Gene expression analysis revealed enhanced expression of CB1 and CB2 genes associated with improved eating behavior and cognition, while POMC expression was reduced. Insulin-polymer treatment restored cognitive function and decreased hyperactivity in the AN-like model.

CONCLUSION

The PSA-RA-based insulin delivery system effectively restores metabolic balance, body weight, and cognitive function in the AN model. Its ability to steadily release insulin makes it a promising candidate for AN treatment."

Effects of Wheat Biscuits Enriched with Plant Proteins Incorporated into an Energy-Restricted Dietary Plan on Postprandial Metabolic Responses of Women with Overweight/Obesity

This study investigates the effect of daily consumption of wheat biscuits enriched with plant proteins in postprandial metabolic responses of women with overweight/obesity who follow an energy-restricted diet. Thirty apparently healthy women participated in a 12-week randomized controlled trial and were assigned either to a control (CB) or an intervention (PB) group. Participants consumed daily either a conventional (CB) or an isocaloric wheat biscuit enriched with plant proteins (PB) containing high amounts of amino acids with appetite-regulating properties, i.e., BCAAs and L-arg. At baseline and the end of the intervention, a mixed meal tolerance test was performed. The responses of glucose, insulin, ghrelin, GLP-1, and glicentin were evaluated over 180 min. After 12 weeks, both groups experienced significant decreases in body weight, fat mass, and waist circumference. In the PB group, a trend towards higher weight loss was observed, accompanied by lower carbohydrate, fat, and energy intakes (p < 0.05 compared to baseline and CB group), while decreases in fasting insulin and the HOMA-IR index were also observed (p < 0.05 compared to baseline). In both groups, similar postprandial glucose, ghrelin, and GLP-1 responses were detected, while iAUC for insulin was lower (p < 0.05). Interestingly, the iAUC of glicentin was greater in the PB group (p < 0.05 compared to baseline). Subjective appetite ratings were beneficially affected in both groups (p < 0.05). Consumption of wheat biscuits enriched in plant proteins contributed to greater weight loss, lower energy intake, and insulin resistance and had a positive impact on postprandial glicentin response, a peptide that can potentially predict long-term weight loss and decreased food intake.

Effects of a high-fat and high-carbohydrate diet on appetite regulation and central AMPK in the hypothalamus of blunt snout bream (Megalobrama amblycephala)

Adenosine monophosphate-activated protein kinase (AMPK) is a sensor of cellular energy changes and controls food intake. This study investigates the effect of a high-calorie diet (high fat diet [HFD], high carbohydrate diet [HCD] and high energy diet [HED]) on appetite and central AMPK in blunt snout bream. In the present study, fish (average initial weight 45.84 ± 0.07 g) were fed the control, HFD, HCD and HED in four replicates for 12 weeks. At the end of the feeding trial, the result showed that body mass index, specific growth rate, feed efficiency ratio and feed intake were not affected (p > 0.05) by dietary treatment. However, fish fed the HFD obtained a significantly higher (p < 0.05) lipid productive value, lipid gain and lipid intake than those fed the control diet, but no significant difference was attributed to others. Also, a significantly higher (p < 0.05) energy intake content was found in fish-fed HFD, HCD and HED than those given the control diet. Long-term HFD and HCD feeding significantly increased (p < 0.05) plasma glucose, glycated serum protein, advanced glycation end product, insulin and leptin content levels than the control group. Moreover, a significantly lower (p < 0.05) complex 1, 2 and 3 content was found in fish-fed HFD and HCD than in the control, but no differences (p > 0.05) were attributed to those in HED. Fish-fed HED significantly upregulated (p < 0.05) hypothalamic ampα 1 and ampα 2 expression, whereas the opposite trend was observed in the hypothalamic mammalian target of rapamycin than those in HFD and HCD compared to the control. However, hypothalamic neuropeptide y, peroxisome proliferator-activated receptor α (pparα), acetyl-coa oxidase and carnitine palmitoyltransferase 1 were significantly upregulated (p < 0.05) in the HCD group, while the opposite was seen in cholecystokinin expression compared to those in the control group. Our findings indicated that the central AMPK signal pathway and appetite were modulated according to the diet's energy level to regulate nutritional status and maintain energy homoeostasis in fish.

Microbial-Based Bioactive Compounds to Alleviate Inflammation in Obesity

The increased prevalence of obesity with several other metabolic disorders, including diabetes and non-alcoholic fatty liver disease, has reached global pandemic proportions. Lifestyle changes may result in a persistent positive energy balance, hastening the onset of these age-related disorders and consequently leading to a diminished lifespan. Although suggestions have been raised on the possible link between obesity and the gut microbiota, progress has been hampered due to the extensive diversity and complexities of the gut microbiota. Being recognized as a potential biomarker owing to its pivotal role in metabolic activities, the dysregulation of the gut microbiota can give rise to a persistent low-grade inflammatory state associated with chronic diseases during aging. This chronic inflammatory state, also known as inflammaging, induced by the chronic activation of the innate immune system via the macrophage, is controlled by the gut microbiota, which links nutrition, metabolism, and the innate immune response. Here, we present the functional roles of prebiotics, probiotics, synbiotics, and postbiotics as bioactive compounds by underscoring their putative contributions to (1) the reduction in gut hyperpermeability due to lipopolysaccharide (LPS) inactivation, (2) increased intestinal barrier function as a consequence of the upregulation of tight junction proteins, and (3) inhibition of proinflammatory pathways, overall leading to the alleviation of chronic inflammation in the management of obesity.

Interaction between high-intensity interval training and high-protein diet on gut microbiota composition and body weight in obese male rats

Diet and exercise are two critical factors that regulate gut microbiota, affecting weight management. The present study investigated the effect of 10 weeks of high-intensity interval training (HIIT) and a high-protein diet (HPD) on gut microbiota composition and body weight changes in obese male Wistar rats. Forty obese rats were randomly divided into five groups, including HPD, HIIT + HPD, HIIT + high-fat diet (HFD) (continuing HFD during intervention), obese control 1 (continuing HFD during intervention), obese control 2 (cutting off HFD at the beginning of the intervention and continuing standard diet), and eight non-obese Wistar rats as a non-obese control (NOC) group (standard diet). Microbial community composition and diversity analysis by sequencing 16S rRNA genes derived from the fecal samples, body weight, and Lee index were assessed. The body weight and Lee index in the NOC, HIIT + HFD, HPD, and HIIT + HPD groups were significantly lower than that in the OC1 and OC2 groups along with the lower body weight and Lee index in the HPD and HIIT + HPD groups compared with the HIIT + HFD group. Also, HFD consumption and switching from HFD to a standard diet or HPD increased gut microbiota dysbiosis. Furthermore, HIIT along with HFD increased the adverse effects of HFD on gut microbiota, while the HIIT + HPD increased microbial richness, improved gut microbiota dysbiosis, and changed rats' phenotype to lean. It appears that HFD discontinuation without doing HIIT does not improve gut microbiota dysbiosis. Also, the HIIT + HFD, HPD, and HIIT + HPD slow down HFD-induced weight gain, but HIIT + HPD is a more reliable strategy for weight management due to its beneficial effects on gut microbiota composition.

Postprandial Glucose and Gastrointestinal Hormone Responses of Healthy Subjects to Wheat Biscuits Enriched with L-Arginine or Branched-Chain Amino Acids of Plant Origin

The study investigates the effects of wheat biscuits supplemented with plant flours originating from legumes/seeds enriched either in L-arginine (L-arg) or branched-chain amino acids (BCAAs) on postprandial glucose response of healthy subjects. Gastrointestinal hormone and amino acid responses as well as subjective appetite sensations are also evaluated. Subjects consumed wheat-based biscuits, enriched either in L-arg (ArgB) or BCAAs (BCAAsB) or a conventional wheat biscuit (CB) or a glucose solution (GS) in an acute randomized crossover design. Responses of glucose, insulin, ghrelin, glucagon-like peptide-1 (GLP-1), peptide YY (PYY) and glicentin, as well as those of L-arginine, L-leucine, L-isoleucine and L-valine, were evaluated over 180 min. Consumption of ArgB and BCAAsB elicited lower glucose iAUC compared to GS (p < 0.05). A lower iAUC for insulin was observed after consumption of BCAAsB (p < 0.05 compared to CB and ArgB), while ArgB elicited higher iAUC for GLP-1 accompanied by higher glicentin response (p < 0.05 compared to CB). BCAAsB and ArgB increased postprandial amino acid concentrations and caused stronger satiety effects compared to CB. Increasing protein content of wheat biscuits with supplementation of plant flours originating from legumes/seeds decreases postprandial glycemia and provides with healthier snack alternatives which can easily be incorporated into diet.

Transcription and proteome changes involved in re-innervation muscle following nerve crush in rats

Severe peripheral nerve injury leads to the irreparable disruption of nerve fibers. This leads to disruption of synapses with the designated muscle, which consequently go through progressive atrophy and damage of muscle function. The molecular mechanism that underlies the re-innervation process has yet to be evaluated using proteomics or transcriptomics. In the present study, multi-dimensional data were therefore integrated with transcriptome and proteome profiles in order to investigate the mechanism of re-innervation in muscles. Two simulated nerve injury muscle models in the rat tibial nerve were compared: the nerve was either cut (denervated, DN group) or crushed but with the nerve sheath intact (re-innervated, RN group). The control group had a preserved and intact tibial nerve. At 4 weeks, the RN group showed better tibial nerve function and recovery of muscle atrophy compared to the DN group. As the high expression of Myh3, Postn, Col6a1 and Cfi, the RN group demonstrated superior re-innervation as well. Both differentially expressed genes (DEGs) and proteins (DEPs) were enriched in the peroxisome proliferator-activated receptors (PPARs) signaling pathway, as well as the energy metabolism. This study provides basic information regarding DEGs and DEPs during re-innervation-induced muscle atrophy. Furthermore, the crucial genes and proteins can be detected as possible treatment targets in the future.

Association Between the Risk of Hyperuricemia and Changes in Branched-Chain Amino Acids Intake Over Twelve Years: A Latent Class Trajectory Analysis From the China Health and Nutrition Survey, 1997-2009

Objective

This study aims to identify dietary branched-chain amino acids (BCAA) consumption trajectories in Chinese adults and to evaluate their association with the risk of hyperuricemia (HU).

Methods

Cohort data from the China Health and Nutrition Survey 1997–2009 were adopted in this research. A total of 6,810 participants aged ≥18 years were included in this study. Participants were designated into four subgroups on basis of the trajectories of dietary BCAA consumption. Cox proportional hazards models were performed to discuss the relationships between varied trajectories and the risk of HU after adjusting potential confounders. The intermediary effect of differential blood indexes between the trajectories and the risk of HU was explored with mediation analysis.

Results

Four distinct trajectory groups of dietary BCAA consumption were identified. Compared with the low stable trajectory group, high to low trajectory group was greatly related to an increased risk of HU (HR 1.35 (95% CI 1.03 to 1.79)) with modification for covariates. Total cholesterol (TC), hemoglobin A1c (HbA1c), fasting blood glucose (FBG), and triglyceride (TG) partially regulated trajectories and HU.

Conclusion

Gradually decreasing dietary BCAA intake increased the risk of HU, which is, at least, partially mediated by TC, HbA1c, FBG, and TG levels.

Wheat Biscuits Enriched with Plant-Based Protein Contribute to Weight Loss and Beneficial Metabolic Effects in Subjects with Overweight/Obesity

The present study aimed to assess the impact of daily consumption of a snack fortified with plant proteins with high content in amino acids with appetite regulating properties (BCAAs and L-arginine), as part of a dietary intervention, on weight loss. Seventy adults without diabetes (26 male, 44 female) and with overweight/obesity participated in a 12-week restricted dietary intervention and were randomized to either a control or an intervention group, consuming daily 70 g of conventional wheat biscuits (CB) or an isocaloric amount of wheat biscuits enriched with plant proteins (PB) originating from legumes and seeds, respectively. Anthropometric characteristics were measured and venous blood samples were collected at baseline and at the end of the intervention. Decreases in body weight, body fat mass and waist circumference were observed in both groups. Participants in the intervention group experienced greater weight loss (7.6 ± 2.7 vs. 6.2 ± 2.7%, p = 0.025) and marginally significant larger decrease in body fat mass (4.9 ± 2.2 vs. 3.9 ± 2.4 kg, p = 0.059). A moderate reduction in IL-1β levels (p = 0.081), a significantly higher decrease in TNF-α levels (p < 0.001) and a marginally significant greater leptin decrease (p = 0.066) in subjects of the PB group were noticed. Greater reductions in caloric and carbohydrate intake and a trend towards a higher decrease in fat intake were also observed in participants of this group. Incorporation of plant-based proteins with high content in amino acids with appetite-regulating properties in wheat biscuits may contribute to greater weight loss and improvement of metabolic parameters in subjects who are overweight or obese. Protein enrichment of snacks offers a beneficial qualitative manipulation that could be successfully incorporated in a diet plan.

Insulin normalized brain metabolic status on a Model of Anorexia Nervosa in Mice

INTRODUCTION

Anorexia nervosa is a psycho-socio-biological disease, characterized by self-starvation and distorted perception of body weight. Patients often over-exercise. Insulin is an anabolic hormone that increases food intake and restores body fat and is present in low levels in anorexia nervosa patients: thus may have therapeutic potential in treating anorexia nervosa.

AIMS

to explore whether low levels insulin administration may result in recovery of cerebral function and restoration of metabolic disorder providing a treatment option for anorexia nervosa.

METHODS

Female Sabra mice maintained on DR of 2.0 hours per day for 32 days, in cages with or without wheel attached to an electronic counter (activity wheel). They were then permitted to eat ad libitum for additional 15 days. On the second week, mice were injected ip with 0.5U/kg long acting Insulin(Lantus) or saline and cognitive function was evaluated. Insulin administered three times a week during days 8-32. Mice euthanized on day 48 and cerebral levels of monoamines, 2-AG and expression of genes associated with metabolic status were evaluated.

RESULTS

Activity wheel mice decreased body weight, 2-AG, dopamine levels and 5-HT1A and increased Camkk2 and SIRT1 gene expression compared to mice without it. Insulin increased body weight, decreased revolutions, enhanced NPY and normalized Camkk2, SIRT-1, BDNF, elevated 2-AG and improved cognition in the wheel group.

CONCLUSION

low dose insulin administration to animal model of anorexia associated with exercise, led to alterations and normalization in brain metabolic status and improved cognition. Insulin should be further explored as potential novel treatment for anorexia nervosa.

The influence of thyroid state on hypothalamic AMP-activated protein kinase pathways in broilers

To investigate whether there are important interactions in play in broilers between thyroid hormones and the central regulation of energy homeostasis through AMP-activated protein kinase (AMPK), we induced a functional hyperthyroid and hypothyroid state in broiler chicks, and quantified systemic and hypothalamic AMPK related gene expression and related protein. Thyroid state was manipulated through dietary supplementation of triiodothyronine (T₃) or methimazole (MMI) for 7 days. A hypothalamic AMPK suppressor, 0.1% α-lipoic acid (α-LA) was used to assess the effects of the T₃ and MMI feed formulations on the AMPK pathways. Feed intake and body weight were reduced in both hypothyroid and hyperthyroid conditions. In hyperthyroid conditions (T₃ supplementation) expression of the AMPKα1 subunit increased, while in hypothyroid conditions (MMI supplementation) active phosphorylated AMPK levels in the hypothalamus dropped, but gene expression of the AMPKα1 and α2 subunit increased. For FAS and ACC (involved in fatty acid metabolism), and CRH, TRH and CNR1 (anorexigenic neuropeptides stimulating energy expenditure) there were indications that their regulation in response to thyroid state might be modulated through AMPK pathways. Our results indicate that the expression of hypothalamic AMPK as well as that of several other genes from AMPK pathways are involved in thyroid-hormone-induced changes in appetite, albeit differently according to thyroid state.

The AMPK-mTOR signaling pathway is involved in regulation of food intake in the hypothalamus of stressed chickens

Glucocorticoids (GCs) can stimulate the appetite and AMPK in broilers. The activation of hypothalamic mTOR has been proposed as an important anorexigenic signal. However, inhibitory effect of AMPK activity on appetite and AMPK downstream signaling pathway under stress has not been reported. In this study, we performed an intracerebroventricular (icv) injection of compound C, an AMPK inhibitor, in GC-treated birds to explore the regulatory mechanism on appetite and AMPK downstream signaling pathway. A total of 48 7-day-old broilers, which had received an icv cannula, were randomly subjected to one of two treatments: subcutaneous injection of dexamethasone (DEX) or saline. After 3 days of continuous DEX injection, chicks of each group received an icv injection with either compound C (6 μg/2 μL) or vehicle (dimethyl sulfoxide, 2 μL). The results showed that body weight gain was reduced by the DEX treatment. Compared with the control, icv injection of compound C reduced feed intake at 0.5-1.5 h. In the DEX-treated group, the inhibitory effect of compound C on appetite remained apparent at 0.5-1 h. The DEX treatment increased the gene expression of liver kinase B1 (LKB1), neuropeptide Y (NPY), and decreased p-mTOR protein level. In stressed broilers, inhibition of AMPK relieved the decreased mTOR activity. A significant interaction was noted in DEX and compound C on protein expression of phospho-AMPK. Taken together, in stressed broilers, the central injection of compound C could inhibit central AMPK activity and reduce appetite, in which the AMPK/mTOR signaling pathway might be involved.

A fifty percent leucine-restricted diet reduces fat mass and improves glucose regulation

Background

Leucine deprivation modulates the dietary amino acid composition, reducing the fat content and improving the glucose tolerance, thus protecting the organism against obesity. However, a complete deprivation of leucine can lead to an extremely rapid fat loss in mice, accompanied by prolonged adverse effects such as weakness and mental fatigue. Therefore, in this study we aimed to seek the optimal concentration of dietary leucine that can reduce fat mass and improve the metabolism without the onset of severe effects.

Methods

To investigate whether there is a better concentration of diet leucine restriction (LR), based on the diet we conducted (A10021B), that can reduce fat mass and improve metabolism status without taking many negative effects, we fed 8 weeks old male C57Bl/6J mice with increasing degrees of leucine restriction diet 0% LR (control group), 25% LR, 50% LR, and 75% LR groups (4–6 mice each group). Fat mass and blood glucose levels were measured. The expression levels of genes involved in lipid metabolism in white adipose tissue (WAT) and liver, and proteins in insulin signaling were assessed in WAT, liver and muscle.

Results

We found that the 50% LR group is the most proper group here at the lowest leucine effective concentration, which reduced fat mass (p < 0.05) and improved glucose regulation in mice over a 90 days feeding. Further studies revealed that lipid synthesis pathway (Fas, Scd1and Srebp1, p < 0.05) was downregulated and lipolysis (Atgl, p < 0.05) was upregulated in WAT in 50% LR group, compared to that in control group. Furthermore, glucose regulation (glucose tolerance test, p < 0.05) was also improved, and insulin signaling (p < 0.05) in the muscle was enhanced in 50% LR group while in WAT and liver were not changed.

Conclusions

Collectively, a 50% LR in mice reduced fat mass and improved glucose regulation, which may function through modulating lipid synthesis and lipolysis pathway in adipose tissue as well as enhancing insulin signaling in muscle. So far, we provide a further consideration for carrying out the diet of leucine restriction to reduce fat and improve metabolism status before clinical study.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12986-021-00564-1.

High protein diet: benefits and risks

The nature of human nutrition has become increasingly important as an effective element in the prevention and treatment of many pathologies, especially obesity, type 2 diabetes and cardiovascular diseases. High protein diets are some of the most popular eating patterns and the Dukan diet has taken the lead in popularity among the diets of this type. An increase of protein in the diet is effective in reducing body weight, primarily due to the loss of adipose tissue, without a significant effect on muscle mass. Another advantage of a high-protein diet is earlier and longer satiety compared to other diets, which makes it comfortable for use. Besides obesity, high protein diets are presumably effective for treating such diseases as nonalcoholic fatty liver disease, diabetes mellitus and cardiovascular diseases However, despite the important advantages, this nutritional model is not universal and is contraindicated in patients with diseases of liver, kidneys and osteoporosis. Besides, the prolonged use of a high protein diet may increase the risks of urolithiasis and reduced mineral bone density even for healthy individuals. Thus, the increase in the proportion of protein in the diet should take place exclusively under the supervision of a physician.

mTOR - Mediated protein synthesis by inhibiting protein catabolism in Chinese perch (Siniperca chuatsi)

Activation of the mechanistic target of rapamycin (mTOR) pathway is known to promote protein synthesis by enhancing mRNA translation. However, there have been few literatures on the effect of mTOR on protein metabolism in non-mammals. The main source of ammonia in fish comes from protein catabolism. The key step of protein catabolism involves the deamination and/or transamination of amino acids. This study is aimed to explore the mechanism underlying mTOR pathway influencing protein retention from the perspective of protein catabolism. Chinese perch were fasted for 24 h and divided into 4 groups randomly before intracerebroventricular (ICV) injection: (1) control group for leucine; (2) leucine group; (3) control group for leucine and rapamycin; (4) leucine and rapamycin group. Food intake was equivalent between each control and treatment groups at each time point (0.5, 4, 12 and 24 h post-injection). Ammonia-N excretion rate, blood glucose, S6 phosphorylation level, and expression of relative genes of protein catabolism (GDH, AMPD, AST, ALT) were determined. The results indicated that the pS6 level was increased, and that the ammonia-N excretion rate, blood glucose, and mRNA level of protein catabolism genes (GDH and AMPD) were significantly decreased after injection with leucine, while those changes were reversed after injection with leucine and rapamycin. Our study not only reveals the mechanism by which mTOR mediates protein synthesis by inhibiting protein catabolism in Chinese perch, but also provides reference for improving the utilization of feed protein.

Evaluation of an Amino Acid Mix on the Secretion of Gastrointestinal Peptides, Glucometabolic Homeostasis, and Appetite in Obese Adolescents Administered with a Fixed-Dose or ad Libitum Meal

Proteins have been demonstrated to reduce food intake in animals and humans via peripheral and central mechanisms. Supplementation of a dietetic regimen with single or mixed amino acids might represent an approach to improve the effectiveness of any body weight reduction program in obese subjects. The aim of the present study was to evaluate the effects of an amino acid mix (L-arginine + L-leucine + L-glutamine + L-tryptophan) on the secretion of some gastrointestinal peptides (i.e., ghrelin and glucagon-like peptide type 1, GLP-1), glucometabolic homeostasis (i.e., glucose, insulin, and glucagon), and appetite (hunger/satiety scored by visual analogue scale, VAS) in obese adolescents (n = 14; 10 females and 4 males; age: 16.6 ± 1.0 years; body mass index (BMI): 36.4 ± 4.6 kg/m²; fat-free mass (FFM): 54.9 ± 4.7%; fat mass (FM): 45.1 ± 4.4%) administered with a fixed-dose (lunch) or ad libitum (dinner) meal. Isocaloric maltodextrins were used as control treatment. During the lunch test, a significant increase in circulating levels of GLP-1, but not of ghrelin, was observed in the amino acid-treated group, which was congruent with significant changes in appetite, i.e., increase in satiety and decrease in hunger. A significant hyperglycemia was found in the maltodextrin-treated group during the prelunch period, without any significant changes in insulin and glucagon between the two groups. During the dinner test, there were no significant differences in appetite (hunger/satiety) and intake of calories. In conclusion, L-arginine, L-leucine, L-glutamine, and L-tryptophan, when administered to obese adolescents with a fixed-dose meal, are capable of evoking an anorexigenic response, which is, at least in part, mediated by an increase in GLP-1 released in circulation by L cells, which are capable of chemosensing specific amino acids present in the intestinal lumen. Further additional studies are requested to understand whether higher doses are necessary to inhibit ad libitum feeding.

Adipocyte-derived extracellular vesicles modulate appetite and weight through mTOR signalling in the hypothalamus

AIM

Type 2 diabetes and obesity are diseases related to surplus energy in the body. Abnormal interaction between the hypothalamus and adipose tissues is a key trigger of energy metabolism dysfunction. Extracellular vesicles (EVs) regulate intercellular communication by transporting intracellular cargo to recipient cells thereby altering the function of recipient cells. This study aimed to evaluate whether adipocyte-derived EVs can act on hypothalamic neurons to modulate energy intake and to identify the EV-associated non-coding RNAs.

METHODS

Confocal imaging was used to trace the uptake of labelled adipocyte-derived exosomes by hypothalamic anorexigenic POMC neurons. The effects of adipocyte-derived EVs on the mammalian target of rapamycin (mTOR) signalling pathway in POMC neurons were evaluated based on mRNA and protein expression in vitro using quantitative real-time PCR and western blotting. In addition, adipocyte-derived EVs were injected into recipient mice, and changes in mice body weight and daily food intake were monitored. The biological effects of the EV-associated MALAT1 on POMC neurons were explored.

RESULTS

Adipocyte-derived EVs were successfully transferred into POMC neurons in vitro. Results showed that adipocytes of obese mice secreted MALAT1-containing EVs, which increased appetite and weight when administered to lean mice. Conversely, adipocyte-derived EVs from lean mice decreased food intake and weight when administered to obese mice.

CONCLUSION

Adipocyte-derived EVs play important roles in mediating the interaction between adipocytes and hypothalamic neurons. Adipocyte-derived EVs can regulate POMC expression through the hypothalamic mTOR signalling in vivo and in vitro, thereby affecting body energy intake.

Increased Susceptibility to Obesity and Glucose Intolerance in Adult Female Rats Programmed by High-Protein Diet during Gestation, But Not during Lactation

Fetal and early postnatal nutritional environments contribute to lifelong health. High-protein (HP) intake in early life can increase obesity risk in response to specific feeding conditions after weaning. This study investigated the effects of a maternal HP diet during pregnancy and/or lactation on the metabolic health of offspring. Three groups of dams received a normal-protein (NP, 20E% proteins) diet during gestation and lactation (Control group), an HP diet (55E% proteins) during gestation (HPgest group), or an HP diet during lactation (HPlact group). From weaning until 10 weeks, female pups were exposed to the NP, the HP or the western (W) diet. HPgest pups had more adipocytes (p = 0.009), more subcutaneous adipose tissue (p = 0.04) and increased expression of genes involved in liver fatty acid synthesis at 10 weeks (p < 0.05). HPgest rats also showed higher food intake and adiposity under the W diet compared to the Control and HPlact rats (p ≤ 0.04). The post-weaning HP diet reduced weight (p < 0.0001), food intake (p < 0.0001), adiposity (p < 0.0001) and glucose tolerance (p < 0.0001) compared to the NP and W diets; this effect was enhanced in the HPgest group (p = 0.04). These results show that a maternal HP diet during gestation, but not lactation, leads to a higher susceptibility to obesity and glucose intolerance in female offspring.

Impact of nutrient overload on metabolic homeostasis

Nutrient overload occurs worldwide as a consequence of the modern diet pattern and the physical inactivity that sometimes accompanies it. Cells initiate multiple protective mechanisms to adapt to elevated intracellular metabolites and restore metabolic homeostasis, but irreversible injury to the cells can occur in the event of prolonged nutrient overload. Many studies have advanced the understanding of the different detrimental effects of nutrient overload; however, few reports have made connections and given the full picture of the impact of nutrient overload on cellular metabolism. In this review, detailed changes in metabolic and energy homeostasis caused by chronic nutrient overload, as well as their associations with the development of metabolic disorders, are discussed. Overnutrition-induced changes in key organelles and sensors rewire cellular bioenergetic pathways and facilitate the shift of the metabolic state toward biosynthesis, thereby leading to the onset of various metabolic disorders, which are essentially the downstream manifestations of a misbalanced metabolic equilibrium. Based on these mechanisms, potential therapeutic targets for metabolic disorders and new research directions are proposed.

Dietary Branched-Chain Amino Acids Regulate Food Intake Partly through Intestinal and Hypothalamic Amino Acid Receptors in Piglets

Strategies to increase feed intake are of great importance for producing more meat in swine production. Intestinal and hypothalamic amino acid receptors are found to largely participate in feed intake regulation. The purpose of the current research is to study the function of branched-chain amino acid (BCAA) supplementation in the regulation of feed intake through sensors that can detect amino acids in piglets. Twenty-four piglets were assigned one of four treatments and fed one of the experimental diets for either a short period (Expt. 1) or a long period (Expt. 2): a normal protein diet (NP, 20.04% CP), a reduced-protein diet (RP, 17.05% CP), or a reduced-protein test diet supplemented with one of two doses of BCAAs (BCAA1, supplemented with 0.13% l-isoleucine, 0.09% l-leucine, and 0.23% l-valine; BCAA2, supplemented with the 150% standardized ileal digestibility BCAA requirement, as recommended by the National Research Council (2012)). In Expt. 1, no differences were observed in the feed intake among piglets fed different diets ( P > 0.05). In Expt. 2, compared with the RP group, the feed intake of piglets was significantly increased after sufficient BCAAs were supplemented in the BCAA1 group, which was associated with decreased cholecystokinin secretion ( P < 0.05), down-regulated expression of type-1 taste receptors 1/3 (T1R1/T1R3) in the intestine, as well as increased expression of pro-opiomelanocortin, activated general control nonderepressible 2 (GCN2), and eukaryotic initiation factor 2α (eIF2α) in the hypothalamus ( P < 0.05). However, the feed intake was decreased for unknown reasons when the piglets were fed a BCAA over-supplemented diet. Our study confirmed that a BCAA-deficient diet inhibited feed intake through two potential ways: regulating the amino acid T1R1/T1R3 receptor in the intestine or activating GCN2/eIF2α pathways in the hypothalamus.

Transcriptome analysis for identifying possible causes of post-reproductive death of Sepia esculenta based on brain tissue

BACKGROUND

The subpeduncle lobe/olfactory lobe-optic gland axis is called the endocrine regulation center of cephalopods. However, little is known about the mechanism of the subpeduncle lobe/olfactory lobe-optic gland axis regulate the sexual maturation and post-reproductive death of Sepia esculenta Hoyle.

OBJECTIVES

The primary objective of this study was to provide basic information for revealing the mechanism of the subpeduncle lobe/olfactory lobe-optic axis regulating the rapid post-reproductive death of S. esculenta.

METHODS

In this paper, Illumina sequencing based transcriptome analysis was performed on the brain tissue of female S. esculenta in the three key developmental stages: growth stage (BG), spawning stage (BS), and post-reproductive death stage (BA).

RESULTS

A total of 66.19 Gb Illumina sequencing data were obtained. A comparative analysis of the three stages showed 2609, 3333, and 170 differentially expressed genes (DEGs) in BG-vs-BA, BG-vs-BA, and BS-vs-BA, respectively. The Gene Ontology (GO) enrichment analysis of DEGs revealed that the regulation of cyclin-dependent protein serine/threonine kinase activity, oxidative phosphorylation, and respiratory chain were significantly enriched. The significant enrichment analysis of the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway identified pathways associated with the regulation of death, such as the mammalian target of rapamycin (mTOR) signaling pathway, AMPK signaling pathway, oxidative phosphorylation, and cell cycle.

CONCLUSION

The post-reproductive death of S. esculenta was found to be a complex energy steady-state regulation network system. The mTOR acted as an energy receptor and had a key role in regulating energy homeostasis.

Feeding Stimulation Ability and Central Effects of Intraperitoneal Treatment of L-Leucine, L-Valine, and L-Proline on Amino Acid Sensing Systems in Rainbow Trout: Implication in Food Intake Control

To continue gathering knowledge on the central regulation of food intake in response to amino acids in teleost fish, using as a model rainbow trout (Oncorhynchus mykiss), we evaluated in a first experiment the feeding attractiveness of L-leucine, L-valine, and L-proline offered as an agar gel matrix. In a second experiment, we assessed the effect of intraperitoneal (IP) treatment with the same amino acids on food intake. In a third experiment, we carried out a similar IP administration of amino acids to evaluate the response of amino acid sensing mechanisms in the hypothalamus and telencephalon. Results are discussed in conjunction with an earlier study where leucine and valine were administered intracerebroventricularly (ICV). The attractiveness of amino acids does not appear to relate to their effects on food intake, at least when administrated by-passing ingestion and luminal absorption, since two attractive amino acids resulted in an anorexigenic (Leu) or no effects (Pro) on food intake while a non-attractive amino acid (Val) induced anorexigenic (IP treatment) or orexigenic (ICV treatment) responses. The effects of Leu on food intake might relate to the expression of hypothalamic neuropeptides and result from the direct activation of amino acid sensing systems. In contrast, while valine had few effects on hypothalamic amino acid sensing systems after ICV treatment, a significant amount of parameters become affected by IP treatment suggesting that the effect of Val after IP treatment is indirect. Proline had no relevant effects on amino acid sensing systems, neuropeptide expression, and food intake, which suggest that this amino acid might not have a relevant role in the homeostatic regulation of food intake through hypothalamic mechanisms. In telencephalon, the same amino acid sensing systems operating in hypothalamus appear to be present and respond to Leu and Val, but it is still unclear how they might relate to the control of food intake.

Relationship between estrogen and body composition, energy, and endocrine factors in obese women with normal and low REE

OBJECTIVE

The aim of this study was to investigate the relationship between estrogen and leptin, thyroid (T3), Uncoupling Protein2 (UCP2), sex hormone binding globulin (SHBG), and resting energy expenditure(REE) in obese subjects with normal and low REE, and to investigate the relationship of estrogen with body composition and energy intake.

METHOD

A total 49 subjects (25-50 years old) were selected. Anthropometric measurements, body composition, and resting energy expenditure were measured. Fasted circulating leptin, T3, SHBG and UCP2 levels were also measured. Subjects were divided to three groups: BMI > 30 and low resting energy expenditure (group I, n = 16), BMI > 30 and normal resting energy expenditure (group II, n = 17), and non-obese women as the control group (group III, n = 16).

RESULT

A significant association was observed between estrogen and REE in obese women with normal REE. There was a significant association between estrogen and leptin in groups I (β = 0.98, p < .0001), and II (β = 0.84, P < .0001). However, no significant association was observed between estrogen and T3 and UCP2 protein in the three groups. Regression analyses demonstrated no correlation between fat mass, percent fat mass, and plasma estrogen. Plasma estrogen was not correlated with caloric intake or macronutrients of the diet.

CONCLUSION

Estrogen has been shown to affect metabolism and hemostasis in obesity and increases resting energy expenditure via leptin. Production of UCP2 in PBMC is not affected by estrogen.

Modifying the Dietary Carbohydrate-to-Protein Ratio Alters the Postprandial Macronutrient Oxidation Pattern in Liver of AMPK-Deficient Mice

Background: Hepatic AMP-activated kinase (AMPK) activity is sensitive to the dietary carbohydrate-to-protein ratio. However, the role of AMPK in metabolic adaptations to variations in dietary macronutrients remains poorly understood.Objective: The objective of this study was to determine the role of hepatic AMPK in the adaptation of energy metabolism in response to modulation of the dietary carbohydrate-to-protein ratio.Methods: Male 7-wk-old wild-type (WT) and liver AMPK-deficient (knockout) mice were fed either a normal-protein and normal-carbohydrate diet (NP-NC; 14% protein, 76% carbohydrate on an energy basis), a low-protein and high-carbohydrate diet (LP-HC; 5% protein, 85% carbohydrate), or a high-protein and low-carbohydrate diet (HP-LC; 55% protein, 35% carbohydrate) for 3 wk. During this period, after an overnight fast, metabolic parameters were measured and indirect calorimetry was performed in mice during the first hours after refeeding a 1-g calibrated meal of their own diet in order to investigate lipid and carbohydrate metabolism.Results: Knockout mice fed an LP-HC or HP-LC meal exhibited 24% and 8% lower amplitudes in meal-induced carbohydrate and lipid oxidation changes. By contrast, knockout mice fed an NP-NC meal displayed normal carbohydrate and lipid oxidation profiles. These mice exhibited a transient increase in hepatic triglycerides and a decrease in hepatic glycogen. These changes were associated with a 650% higher secretion of fibroblast growth factor 21 (FGF21) 2 h after refeeding.Conclusions: The consequences of hepatic AMPK deletion depend on the dietary carbohydrate-to-protein ratio. In mice fed the NP-NC diet, deletion of AMPK in the liver led to an adaptation of liver metabolism resulting in increased secretion of FGF21. These changes possibly compensated for the absence of hepatic AMPK, as these mice exhibited normal postprandial changes in carbohydrate and lipid oxidation. By contrast, in mice fed the LP-HC and HP-LC diets, the lack of adjustment in liver metabolism in knockout mice resulted in a metabolic inflexibility, leading to a reduced amplitude of meal-induced changes in carbohydrate and lipid oxidation.

Nutrient Sensing: Another Chemosensitivity of the Olfactory System

Olfaction is a major sensory modality involved in real time perception of the chemical composition of the external environment. Olfaction favors anticipation and rapid adaptation of behavioral responses necessary for animal survival. Furthermore, recent studies have demonstrated that there is a direct action of metabolic peptides on the olfactory network. Orexigenic peptides such as ghrelin and orexin increase olfactory sensitivity, which in turn, is decreased by anorexigenic hormones such as insulin and leptin. In addition to peptides, nutrients can play a key role on neuronal activity. Very little is known about nutrient sensing in olfactory areas. Nutrients, such as carbohydrates, amino acids, and lipids, could play a key role in modulating olfactory sensitivity to adjust feeding behavior according to metabolic need. Here we summarize recent findings on nutrient-sensing neurons in olfactory areas and delineate the limits of our knowledge on this topic. The present review opens new lines of investigations on the relationship between olfaction and food intake, which could contribute to determining the etiology of metabolic disorders.

Molecular mechanisms of appetite and obesity: a role for brain AMPK

Feeding behaviour and energy storage are both crucial aspects of survival. Thus, it is of fundamental importance to understand the molecular mechanisms regulating these basic processes. The AMP-activated protein kinase (AMPK) has been revealed as one of the key molecules modulating energy homoeostasis. Indeed, AMPK appears to be essential for translating nutritional and energy requirements into generation of an adequate neuronal response, particularly in two areas of the brain, the hypothalamus and the hindbrain. Failure of this physiological response can lead to energy imbalance, ultimately with extreme consequences, such as leanness or obesity. Here, we will review the data that put brain AMPK in the spotlight as a regulator of appetite.

Effects of a whey protein supplementation on oxidative stress, body composition and glucose metabolism among overweight people affected by diabetes mellitus or impaired fasting glucose: A pilot study

Obesity and diabetes mellitus type 2 (DM2) are characterized by chronic inflammation and oxidative stress [Donath et al. 2013] and this leads to cardiovascular diseases [Hulsmans & Holvoet 2010]. Whey proteins (WP) have antioxidant [Chitapanarux et al. 2009], anti-inflammatory [Sugawara et al. 2012] and hypoglycemic activities [Mignone et al. 2015], while data on weight, body composition [Frestedt et al. 2008; Aldrich et al. 2011] and blood pressure are conflicting [Kawase et al. 2000; Lee et al. 2007]. WP have unpleasant taste and smell [Patel 2015], but a new WP isolate (ProLYOtin®) seems to be more palatable. 40 g/die of ProLYOtin® were supplemented to overweight people (n=31) with impaired fasting glucose/DM2 for 12 weeks. Markers of antioxidant status (total antioxidant status, glutathione peroxidase, glutathione reductase, uric acid), oxidative damage (thiobarbituric acid reactive substances, advanced oxidation protein products, 8-hydroxydeoxyguanosine), inflammation (interleukin-6, high sensitive reactive protein C) and glicemic status (fasting glucose, insulin, glycated hemoglobin), anthropometric data (weight, height, waist circumference), body composition (body cell mass, fat mass), blood pressure, hand grip strength and skin autofluorescence were measured before and at the end of supplementation. Isolate palatability was evaluated. An increase in glutathione peroxidase, a decrease in uric acid and no change in glutathione reductase, total antioxidant status, oxidative damage, inflammation and glucose markers were found. Significant improvements in anthropometric parameters and fat mass were detected. There wasn't any change in blood pressure, skin autofluorescence and physical performance. Two-thirds of subjects judged the supplement positively. ProLYOtin® seems suitable for treatment of OS and overweight.

Acute and Long-Term Impact of High-Protein Diets on Endocrine and Metabolic Function, Body Composition, and Exercise-Induced Adaptations

BACKGROUND

High-protein diets have been shown to improve body composition through alterations in satiety, muscle protein synthesis, and the thermic effect of food.

AIM

Given these findings, the purpose of this review is to discuss the integration of the specific hormonal and metabolic effects of high-protein diets following both acute and long-term usage, especially with regard to body composition.

METHODS

Full-text articles were obtained through PubMed by using the terms "high-protein diet and body composition," "high-protein diet and exercise," "high-protein diet risk," "high-protein diet side effects," "protein quality PDCAAS," "RDA for protein," and "daily protein recommendation." Articles were initially screened according to their title and abstract; careful evaluation of the full manuscripts was then used to identify relevant articles.

RESULTS

The higher satiety exerted by high-protein diets is generated through increments in anorexigenic, as well as decrements in orexigenic hormones. Improvements in muscle mass are achieved by activation of muscle protein synthesis acting through the mTOR pathway. High thermic effect of food is caused due to necessary deamination, gluconeogenesis, and urea synthesis caused by high-protein diets. Interestingly, high-protein diets in both hypo- and normocaloric conditions have shown to improve body composition, whereas in combination with hypercaloric conditions does not seem to increase fat mass, when the excess energy comes from protein.

CONCLUSIONS

High protein diets effectively improve body composition by acting through different pathways.

Animal Models for the Study of the Relationships between Diet and Obesity: A Focus on Dietary Protein and Estrogen Deficiency

Obesity is an increasing major public health concern asking for dietary strategies to limit weight gain and associated comorbidities. In this review, we present animal models, particularly rats and mice, which have been extensively used by scientists to understand the consequences of diet quality on weight gain and health. Notably, modulation of dietary protein quantity and/or quality has been shown to exert huge effects on body composition homeostasis through the modulation of food intake, energy expenditure, and metabolic pathways. Interestingly, the perinatal window appears to represent a critical period during which the protein intake of the dam can impact the offspring’s weight gain and feeding behavior. Animal models are also widely used to understand the processes and mechanisms that contribute to obesity at different physiological and pathophysiological stages. An interesting example of such aspect is the situation of decreased estrogen level occurring at menopause, which is linked to weight gain and decreased energy expenditure. To study metabolic disorders associated with such situation, estrogen withdrawal in ovariectomized animal models to mimic menopause are frequently used. According to many studies, clear species-specific differences exist between rats and mice that need to be taken into account when results are extrapolated to humans.

Linking Gut Microbiota and Inflammation to Obesity and Insulin Resistance

Obesity and insulin resistance are the major predisposing factors to comorbidities, such as Type 2 diabetes, nonalcoholic fatty liver disease, cardiovascular and neurodegenerative diseases, and several types of cancer. The prevalence of obesity is still increasing worldwide and now affects a large number of individuals. Here, we review the role of the gut microbiota in the pathophysiology of insulin resistance/obesity. The human intestine is colonized by ∼100 trillion bacteria, which constitute the gut microbiota. Studies have shown that lean and overweight rodents and humans may present differences in the composition of their intestinal flora. Over the past 10 years, data from different sources have established a causal link between the intestinal microbiota and obesity/insulin resistance. It is important to emphasize that diet-induced obesity promotes insulin resistance by mechanisms independent and dependent on gut microbiota. In this review, we present several mechanisms that contribute to explaining the link between intestinal flora and insulin resistance/obesity. The LPS from intestinal flora bacteria can induce a chronic subclinical inflammatory process and obesity, leading to insulin resistance through activation of TLR4. The reduction in circulating SCFA may also have an essential role in the installation of reduced insulin sensitivity and obesity. Other mechanisms include effects of bile acids, branched-chain amino acids (BCAA), and some other lesser-known factors. In the near future, this area should open new therapeutic avenues for obesity/insulin resistance and its comorbidities.

Eat and Death: Chronic Over-Eating

Obesity-related co-morbidities decrease life quality, reduce working ability and lead to early death. The total amount of dietary fat consumption may be the most potent food-related risk factor for weight gain. In this respect, dietary intake of high-caloric, high-fat diets due to chronic over-eating and sedentary lifestyle lead to increased storage of triglycerides not only in adipose tissue but also ectopically in other tissues . Increased plasma concentrations of non-esterified free fatty acids and lipid-overloaded hypertrophic adipocytes may cause insulin resistance in an inflammation-independent manner. Even in the absence of metabolic disorders, mismatch between fatty acid uptake and utilization leads to the accumulation of toxic lipid species resulting in organ dysfunction. Lipid-induced apoptosis, ceramide accumulation, reactive oxygen species overproduction, endoplasmic reticulum stress, and mitochondrial dysfunction may play role in the pathogenesis of lipotoxicity. The hypothalamus senses availability of circulating levels of glucose, lipids and amino acids, thereby modifies feeding according to the levels of those molecules. However, the hypothalamus is also similarly vulnerable to lipotoxicity as the other ectopic lipid accumulated tissues. Chronic overnutrition most likely provides repetitive and persistent signals that up-regulate inhibitor of nuclear factor kappa B kinase beta subunit/nuclear factor kappa B (IKKβ/NF-κB) in the hypothalamus before the onset of obesity. However, the mechanisms by which high-fat diet induced peripheral signals affect the hypothalamic arcuate nucleus remain largely unknown. In this chapter, besides lipids and leptin, the role of glucose and insulin on specialized fuel-sensing neurons of hypothalamic neuronal circuits has been debated.

Disorders of branched chain amino acid metabolism

The three essential branched-chain amino acids (BCAAs), leucine, isoleucine and valine, share the first enzymatic steps in their metabolic pathways, including a reversible transamination followed by an irreversible oxidative decarboxylation to coenzyme-A derivatives. The respective oxidative pathways subsequently diverge and at the final steps yield acetyl- and/or propionyl-CoA that enter the Krebs cycle. Many disorders in these pathways are diagnosed through expanded newborn screening by tandem mass spectrometry. Maple syrup urine disease (MSUD) is the only disorder of the group that is associated with elevated body fluid levels of the BCAAs. Due to the irreversible oxidative decarboxylation step distal enzymatic blocks in the pathways do not result in the accumulation of amino acids, but rather to CoA-activated small carboxylic acids identified by gas chromatography mass spectrometry analysis of urine and are therefore classified as organic acidurias. Disorders in these pathways can present with a neonatal onset severe-, or chronic intermittent- or progressive forms. Metabolic instability and increased morbidity and mortality are shared between inborn errors in the BCAA pathways, while treatment options remain limited, comprised mainly of dietary management and in some cases solid organ transplantation.

Adaptation to a high-protein diet progressively increases the postprandial accumulation of carbon skeletons from dietary amino acids in rats

We aimed to determine whether oxidative pathways adapt to the overproduction of carbon skeletons resulting from the progressive activation of amino acid (AA) deamination and ureagenesis under a high-protein (HP) diet. Ninety-four male Wistar rats, of which 54 were implanted with a permanent jugular catheter, were fed a normal protein diet for 1 wk and were then switched to an HP diet for 1, 3, 6, or 14 days. On the experimental day, they were given their meal containing a mixture of 20 U-[¹⁵N]-[¹³C] AA, whose metabolic fate was followed for 4 h. Gastric emptying tended to be slower during the first 3 days of adaptation. ¹⁵N excretion in urine increased progressively during the first 6 days, reaching 29% of ingested protein. ¹³CO₂ excretion was maximal, as early as the first day, and represented only 16% of the ingested proteins. Consequently, the amount of carbon skeletons remaining in the metabolic pools 4 h after the meal ingestion progressively increased to 42% of the deaminated dietary AA after 6 days of HP diet. In contrast, ¹³C enrichment of plasma glucose tended to increase from 1 to 14 days of the HP diet. We conclude that there is no oxidative adaptation in the early postprandial period to an excess of carbon skeletons resulting from AA deamination in HP diets. This leads to an increase in the postprandial accumulation of carbon skeletons throughout the adaptation to an HP diet, which can contribute to the sustainable satiating effect of this diet.

Hypothalamic AMPK-induced autophagy increases food intake by regulating NPY and POMC expression

Hypothalamic AMP-activated protein kinase (AMPK) plays important roles in the regulation of food intake by altering the expression of orexigenic or anorexigenic neuropeptides. However, little is known about the mechanisms of this regulation. Here, we report that hypothalamic AMPK modulates the expression of NPY (neuropeptide Y), an orexigenic neuropeptide, and POMC (pro-opiomelanocortin-α), an anorexigenic neuropeptide, by regulating autophagic activity in vitro and in vivo. In hypothalamic cell lines subjected to low glucose availability such as 2-deoxy-d-glucose (2DG)-induced glucoprivation or glucose deprivation, autophagy was induced via the activation of AMPK, which regulates ULK1 and MTOR complex 1 followed by increased Npy and decreased Pomc expression. Pharmacological or genetic inhibition of autophagy diminished the effect of AMPK on neuropeptide expression in hypothalamic cell lines. Moreover, AMPK knockdown in the arcuate nucleus of the hypothalamus decreased autophagic activity and changed Npy and Pomc expression, leading to a reduction in food intake and body weight. AMPK knockdown abolished the orexigenic effects of intraperitoneal 2DG injection by decreasing autophagy and changing Npy and Pomc expression in mice fed a high-fat diet. We suggest that the induction of autophagy is a possible mechanism of AMPK-mediated regulation of neuropeptide expression and control of feeding in response to low glucose availability.

Dietary Supplementation with α-Ketoglutarate Activates mTOR Signaling and Enhances Energy Status in Skeletal Muscle of Lipopolysaccharide-Challenged Piglets

BACKGROUND

Skeletal muscle undergoes rapid loss in response to inflammation. α-Ketoglutarate (AKG) has been reported to enhance muscle growth in piglets, but the underlying mechanisms are largely unknown.

OBJECTIVES

This study tested the hypothesis that dietary AKG supplementation activates mechanistic target of rapamycin (mTOR) signaling and improves skeletal muscle energy metabolism in lipopolysaccharide (LPS)-challenged piglets.

METHODS

Forty-eight male piglets (Duroc × Landrace × Yorkshire) were weaned at 21 d of age to a corn- and soybean meal-based diet. After a 3-d period of adaptation, piglets with a mean weight of 7.21 kg were randomly assigned to control, LPS (intraperitoneal administration of 80 μg LPS/kg body weight on days 10, 12, 14, and 16), or LPS plus 1% dietary AKG (LPS+AKG) groups. On day 16, blood samples were collected from 8 piglets/group 3 h after LPS administration. On day 17, piglets were killed to obtain gastrocnemius muscle from 8 piglets/group for biochemical analysis.

RESULTS

Compared with the control group, LPS administration increased (P < 0.05) plasma concentrations of globulin (by 14%) and tumor necrosis factor α (by 59%) and the intramuscular ratio of AMP to ATP (by 93%) and abundance of phosphorylated acetyl-coenzyme A carboxylase (ACC) β protein (by 64%). Compared with the control group, LPS administration reduced (P < 0.05) weight gain (by 15%); plasma concentrations of glutamine (by 20%), glucose (by 23%), insulin, insulin-like growth factor I, and epidermal growth factor; intramuscular concentrations of glutamine (by 27%), ATP (by 12%), ADP (by 22%), and total adenine nucleotides; and intramuscular ratios of phosphorylated mTOR to total mTOR (by 38%) and of phosphorylated 70-kDa ribosomal protein S6 kinase (p70S6K) to total p70S6K (by 39%). These adverse effects of LPS were ameliorated (P < 0.05) by AKG supplementation.

CONCLUSIONS

Dietary AKG supplementation activated mTOR signaling, inhibited ACC-β, and improved energy status in skeletal muscle of LPS-challenged piglets. These results provide a biochemical basis for the use of AKG to enhance piglet growth under inflammatory or practical postweaning conditions.

Dietary whey reduces energy intake and alters hypothalamic gene expression in obese phyto-oestrogen-deprived male rats

Removing dietary phyto-oestrogens in adult male rats causes obesity and diabetes. As whey proteins have been reported to reduce food intake and improve glucose homoeostasis, we investigated whether they could attenuate susceptibility to obesity and diabetes due to phyto-oestrogen deprivation. To this end, thirty male Wistar rats were fed a high-phyto-oestrogen (HP) or a phyto-oestrogen-free (PF) diet for 10 weeks; six rats from each group were killed. The remaining HP animals (six animals) continued receiving the HP diet for 6 weeks. The remaining PF rats (twelve rats) were divided in two groups: one was given the PF diet and the other a variation of the PF diet plus whey protein (PF-W). Body weight, food intake and adipose tissue weights were recorded. Hypothalamic mRNA expressions of orexigenic (neuropeptide Y, agouti-related protein (AgRP)) and anorexigenic (pro-opiomelanocortin (POMC), cocaine-amphetamine-related transcript (CART)) neuropeptides were quantified by real-time PCR. Serum glucose, insulin and total thyroxine (T4), thyroid-stimulating hormone, testosterone and oestradiol were assessed. After 10 weeks of PF diet, increased body weight, adiposity and energy intake, with up-regulation of AgRP and down-regulation of POMC', were observed. Longer treatment exacerbated these results, increased total T4 levels, reduced oestradiol levels and impaired glucose homoeostasis. PF-W reduced energy intake and increased POMC expression; however, body weight and adiposity remained unchanged. PF-W could not prevent the hormonal changes or the high circulating glucose levels induced by phyto-oestrogen deprivation, but reduced fasting insulin. These data demonstrate that, although 6 weeks of whey administration could not prevent obesity in phyto-oestrogen-deprived rats, the reduction in energy intake and circulating insulin could be beneficial with longer treatments.

Hypothalamic AMPK as a Regulator of Energy Homeostasis

Activated in energy depletion conditions, AMP-activated protein kinase (AMPK) acts as a cellular energy sensor and regulator in both central nervous system and peripheral organs. Hypothalamic AMPK restores energy balance by promoting feeding behavior to increase energy intake, increasing glucose production, and reducing thermogenesis to decrease energy output. Besides energy state, many hormones have been shown to act in concert with AMPK to mediate their anorexigenic and orexigenic central effects as well as thermogenic influences. Here we explore the factors that affect hypothalamic AMPK activity and give the underlying mechanisms for the role of central AMPK in energy homeostasis together with the physiological effects of hypothalamic AMPK on energy balance restoration.

The Macronutrients, Appetite, and Energy Intake

Each of the macronutrients-carbohydrate, protein, and fat-has a unique set of properties that influences health, but all are a source of energy. The optimal balance of their contribution to the diet has been a long-standing matter of debate. Over the past half century, thinking has progressed regarding the mechanisms by which each macronutrient may contribute to energy balance. At the beginning of this period, metabolic signals that initiated eating events (i.e., determined eating frequency) were emphasized. This was followed by an orientation to gut endocrine signals that purportedly modulate the size of eating events (i.e., determined portion size). Most recently, research attention has been directed to the brain, where the reward signals elicited by the macronutrients are viewed as potentially problematic (e.g., contribute to disordered eating). At this point, the predictive power of the macronutrients for energy intake remains limited.

Hypothalamic AMPK: a canonical regulator of whole-body energy balance

AMP-activated protein kinase (AMPK) has a major role in the modulation of energy balance. AMPK is activated in conditions of low energy, increasing energy production and reducing energy consumption. The AMPK pathway is a canonical route regulating energy homeostasis by integrating peripheral signals, such as hormones and metabolites, with neuronal networks. Current evidence has implicated AMPK in the hypothalamus and hindbrain with feeding, brown adipose tissue thermogenesis and browning of white adipose tissue, through modulation of the sympathetic nervous system, as well as glucose homeostasis. Interestingly, several potential antiobesity and/or antidiabetic agents, some of which are currently in clinical use such as metformin and liraglutide, exert some of their actions by acting on AMPK. Furthermore, the orexigenic and weight-gain effects of commonly used antipsychotic drugs are also mediated by hypothalamic AMPK. Overall, this evidence suggests that hypothalamic AMPK signalling is an interesting target for drug development, but is this approach feasible? In this Review we discuss the current understanding of hypothalamic AMPK and its role in the central regulation of energy balance and metabolism.

Hepatic autophagy contributes to the metabolic response to dietary protein restriction

Autophagy is an essential cellular response which acts to release stored cellular substrates during nutrient restriction, and particularly plays a key role in the cellular response to amino acid restriction. However, there has been limited work testing whether the induction of autophagy is required for adaptive metabolic responses to dietary protein restriction in the whole animal. Here, we found that moderate dietary protein restriction led to a series of metabolic changes in rats, including increases in food intake and energy expenditure, the downregulation of hepatic fatty acid synthesis gene expression and reduced markers of hepatic mitochondrial number. Importantly, these effects were also associated with an induction of hepatic autophagy. To determine if the induction of autophagy contributes to these metabolic effects, we tested the metabolic response to dietary protein restriction in BCL2-AAA mice, which bear a genetic mutation that impairs autophagy induction. Interestingly, BCL2-AAA mice exhibit exaggerated responses in terms of both food intake and energy expenditure, whereas the effects of protein restriction on hepatic metabolism were significantly blunted. These data demonstrate that restriction of dietary protein is sufficient to trigger hepatic autophagy, and that disruption of autophagy significantly alters both hepatic and whole animal metabolic response to dietary protein restriction.

Effects of metformin and sitagliptin on glycolipid metabolism in type 2 diabetic rats on different diets

INTRODUCTION

The aim of the study was to investigate the effects of metformin and sitagliptin on glycolipid metabolism in type 2 diabetes after different diets.

MATERIAL AND METHODS

Seventy Male Sprague Dawley rats were fed with a high fat diet followed by streptozotocin treatment to induce type 2 diabetes. Then all rats were randomly divided into a control group, a metformin group (200 mg/kg), and a sitagliptin group (10 mg/kg). Each group was further divided into 4 groups receiving one load of high carbohydrate diet (45% glucose, 4.5 ml/kg), high fat diet (20% lipid emulsion, 4.5 ml/kg), high protein diet (20% whey protein, 10 ml/kg) or mixed meal, respectively. The caloric densities were all 33 kJ/kg. Postprandial blood glucose (P2BG), triglyceride (TG), glucagon-like peptide-1 (GLP-1), glucagon and insulin levels were measured.

RESULTS

In the high carbohydrate group, sitagliptin was more efficient in lowering P2BG compared with metformin (p < 0.05). In the high-fat group, metformin was more powerful in lowering TG (p < 0.05) and P2BG (p < 0.05) levels because of its improvement of insulin sensitivity. In the high protein diet group, metformin did not reduce the P2BG level (p > 0.05), although it did reduce the TG level (p < 0.05). In the mixed diet group, metformin was more efficient in lowering P2BG (p < 0.05) but had a similar effect on TG (p > 0.05) compared with sitagliptin.

CONCLUSIONS

In the type 2 diabetic model, metformin and sitagliptin have different effects on glycolipid metabolism after different diets. If it is proved in type 2 diabetic patients, then different medicines may be recommended according to different diets in order to improve glycolipid metabolism.

Obesity and brain inflammation: a focus on multiple sclerosis

The increase in prevalence of obesity in industrialized societies is an indisputable fact. However, the apparent passive role played by adipocytes, in pathophysiological terms, has been gradually substituted by a metabolically active performance, relevant to many biochemical mechanisms that may contribute to a chronic low-grade inflammatory status, which increasingly imposes itself as a key feature of obesity. This chronic inflammatory status will have to be integrated into the complex equation of many diseases in which inflammation plays a crucial role. Multiple sclerosis (MS) is a chronic inflammatory condition typically confined to the central nervous system, and many work has been produced to find possible points of contact between the biology of this immune-mediated disease and obesity. So far, clinical data are not conclusive, but many biochemical features have been recently disclosed. Brain inflammation has been implicated in some of the mechanisms that lead to obesity, which has also been recognized as an important player in inducing some degree of immune dysfunction. In this review, we collected evidence that allows establishing bridges between obesity and MS. After considering epidemiological controversies, we will focus on possible shared mechanisms, as well as on the potential contributions that disease-modifying drugs may have on this apparent relationship of mutual interference.